Already known are methods for manufacturing sensors, where a plurality of electric layers are deposited on the upper side of a silicon substrate. Starting from the back of the silicon substrate, an opening is then etched which reaches up to the dielectric layers. Usually, a silicon oxide layer is used as the lowest dielectric layer which comes to rest directly on the silicon substrate. This layer has the problem that, during the etching processes used for etching in the opening, the silicon oxide layer is usually slightly attacked. Therefore, the thickness of a membrane produced in such a way cannot be controlled accurately.
The method according to the present invention has the advantage over the related art that the membrane thickness is controlled accurately. This is achieved by particularly simple means.
By using a silicon oxide layer which, in its thickness, is selected such that it is removed during the etching of the opening, an improved adhesion of the silicon nitride layer to the silicon substrate can be achieved. Moreover, the oxide layer acts as mechanical isolation so that mechanical stresses appearing in the nitride layer, for example, during high-temperature processes, are reduced. In this manner, slip lines are prevented in the substrate during subsequent high-temperature steps. A high-temperature step is the reoxidation of the silicon nitride layer, which is used for forming an adhesion-improving silicon oxide layer for subsequent metallization steps. Preferably used as material for the measuring element is platinum, since this material has a well-controllable temperature dependence of the electrical resistance and a good chemical stability. By using further silicon oxide layers, a protection of the metallic measuring element is achieved, and mechanical stresses in the membrane can be adjusted selectively. By embedding intermediate layers of silicon nitride, the stresses in the membrane can be adjusted in a broader range, and a slight moisture absorption can be achieved.